Quick question as to what methods you guys are using to "send in exceptions" Is there a way of contacting hotmail support that doesn't involve an endless loop of "we see no problems" with their tier 1 techs?

I would say the contact with support should be made by the hotmail subscriber. They can claim they don't receive their important mail and want that situation rectified. They have a customer relation with hotmail.

My experience is that contacting services where you are not a customer yourself is usually very difficult and will often not result in any action.

FYI I do already have SPF, PTR and DMARC records published in DNS which has ensured reliable delivery to gmail addresses, but hotmail seems to have their own internal scoring system

Another problem is that hotmail uses a cache for SPF and DMARC and it takes very long to expire. I have seen mail problems in hotmail at least a month after an SPF record was changed to include more valid addresses, and they were still considered invalid (resulting in postmaster report via DMARC info).

Rob